1. Field of the Invention
The invention relates to an apparatus for monitoring the flow of liquid or gaseous media in a pipeline, consisting of a casing and a control element for triggering various switching operations, which element is movably supported in the casing against a resetting force.
2. Description of the Prior Art
Flow monitoring devices which may be installed in or mounted on pipelines serve the purpose of triggering a switching function if either a predetermined amount of flow through the pipe is exceeded or if an insufficient flow condition exists. For this purpose, a deflecting or floating body is movably arranged in the fluid flow path and is pivoted or displaced, depending on the given amount of through-flow. A switch is actuated when a predetermined flow condition is reached, either directly by mechanical means, or in a contactless manner, for example, capacitatively or inductively.
A flow monitor disclosed in German Patent DE-83 06 892 teaches that when the deflecting body is pivoted by the flow medium, its position may be monitored by the magnetic force generated by two counterpoled magnets. In this prior art monitoring device, a magnet is mounted at one end of the flow-deflecting body and a corresponding opposite pole magnet is mounted in the hollow housing or casing of the apparatus. This means that in this known device, the resetting force is not produced by a return spring, as is the case in many of the prior art devices. Use of a return spring has the disadvantage that it is highly dependent upon external influences with respect to its switching behavior. The switching behavior of magnetic forces, on the other hand, remains constant over long periods of time.
However, even with an embodiment using magnetic switches, it has not been possible to prevent the flow monitor function from deteriorating even after a short period of operation. The temperature difference between the hot medium flowing in the pipeline and the relatively cool medium in the hollow housing produces a suction between the pipe or conduit and the housing or casing. This causes a constant exchange or flow medium between the conduit and the casing interior. This results in, particularly if the flow medium is water containing lime, zinc carbonates being deposited in the bearing for that portion of the deflecting body arranged in the casing. These deposits interefere to a great extent with the mobility of the deflecting body, even after a short period of operation, so that it is no longer possible to reach a preset switching point. Furthermore, magnetic particles carried along by the flow medium penetrate the casing and adversely influence the switching behavior because these particles are deposited on the magnets.